1. Field of the Invention
The disclosed embodiments of the present invention relate to a light-emitting diode (LED) driving circuit and related circuit driving method, and more particularly, to an LED driving circuit with a full operational voltage range, a better linear regulating ability and a power factor correction function, and a related circuit driving method thereof.
2. Description of the Prior Art
In the field of illumination, in order to achieve the purpose of energy saving, using lamps with light-emitting diodes (LED) as light sources to replace the traditional fluorescent tube is gradually popular. In general, the LED must be driven through a driving circuit to have the power-saving effect, wherein the driving circuit rectifies the sine wave output voltage of the general mains, and then provides the power to the LED in a periodic manner. Moreover, the current flowing into the LED would be proportional to the amplitude of the output voltage. In other words, the brightness of the LED would be proportional to the amplitude of the output voltage. Hence, the driving circuit must reduce the duty cycle of the LED to make the brightness of the LED remain unchanged. However, the amplitude of output voltage of mains around the world is not consistent. For example, the amplitude of the output voltage may be 110V (volts) or 220V. Hence, the conventional driving circuit can only be used under the output voltage with a single amplitude. Alternatively, an additional boost converter is used to raise the output voltage to a specific voltage, and then supplies the specific voltage to the LED. This implementation, however, would increase the manufacturing cost of the driving circuit. Further, since the driving circuit itself would have a delay time, the driving circuit can not immediately present the voltage variation of the mains in the current of the LED, which degrades the linear regulation performance of the driving circuit.
Therefore, how to design a low-cost LED driving circuit with a full voltage operating range and a better linear regulating ability has become a critical issue to be solved in this field.